It is actually super key thing in the end. You need to be working out in regular deployments to get things smooth and slick on such stuff....2nd nature in the head and training....and also knowing your logistics inside out for each intensity level (and make use of defensive advantage on that etc).
NATO found this out when it analysed REFORGER each time afterwards too (down to minute detail in the before and after to get final %'s on wargame reality and re-insert the lessons in relevant areas)....
i.e which units mobilised and performed the best...which ones did not....and crucially why (and address it). They are really only power at scale that has done this on planet Earth.
The other (non western p5) powers (i.e China and Russia) of note simply have not done so ....because they:
a) need to spend that resource to do so (and trade this off in their mindset with other spending they do in military or non-military domains)...and enjoying bulk deterrence that might be counter-productive to this (compared to smaller and especially threatened-feeling countries).
b) their varying/lacking level of development+experience in military institutions developed to handle and address failures rather than make it "someone elses problem" in the ladder or simply cover it up etc.
Thus it is wartime when these things get called out and fleshed out in the end....for all to see for themselves, whatever the strategy and context that is opted for past it.
Indian mobilisations of scale (brasstacks and then parakram) are somewhat complicated story of their own...again there were major issues baked in.
But China and Russia have not done that kind of mobilisation relative to their force structures (till Russia just did now and now finding out problems real time).
Other countries (of smaller scale) have to keep things rotating well to stay prepped and relevant as they can....and when threatened in some way....often do just that. They generally manage a lot better than bigger countries overall on this as you can imagine.
@Joe Shearer @Paro @AlphaMike
BTW the related contents here also doesn't deserve to be lost in the large RUS-UKR war thread...and may be of use for audience in this thread to get some detail on what people are seeing with the Russian approach (at least in their first phase):